Present work machines, such as track type tractors, may utilize a torque converter to allow the engine to spin somewhat independently of the transmission. Typically, the torque converter acts as a fluid coupler between the engine and the transmission, which transfers torque from the engine through the transmission and eventually to the ground. Because of the natural performance of torque converters, maximum ground speed can't be controlled even if the engine speed were controlled to be constant. This results in the machine speeding up even though the load is decreasing. The problem with traditional engine control is that even though power is decreasing, higher and higher speed ratios are encountered, which cause ground speeds to increase.
Government agencies have put stringent regulations and requirements on the amount of noise that a work machine can emit. Work machines, such as tracked machines are dominated by track noise; therefore, reducing the ground speed is advantageous for reducing noise. Traditionally, this was accomplished by reducing the high idle of the machine. However, this strategy is disadvantaged by the loss in productivity under a range of high speed, high load.
Furthermore, work machines, such as track type tractors, often are equipped with a ripper. When the ripper is engaged in a ripping operation, maintaining a constant speed is difficult because of the fluctuation in loads. The ground speed of the machine will vary based on the constant revolution per minute (RPM) of the engine and the fluctuating load.
One such work machine is disclosed in U.S. Pat. No. 6,240,356 to Robert A. Lapke on May 29, 2001. Lapke discloses a speed control system to maintain the ground speed of the work machine below a pre-determined maximum ground speed limit based on the angle of inclination of the operating terrain.
The present invention is directed to overcoming one or more of the problems set forth above.